As one solution based on a concept of information lifecycle management, hierarchical control on a storage apparatus is known. In this technology, storage devices managed by the storage apparatus for storing information are divided into a plurality of tiers based on its performance (such as responsiveness or reliability), cost, or the like, and the tier to be used to store the information based on a utility value thereof is selected. For example, the storage devices of the storage apparatus are, in other words, a storage area pool provided by those storage device is tiered into three tiers of Tier1, Tier2, and Tier3.
As an example of the hierarchical control, Tier1 is associated with a solid state drive (SSD), Tier2 is associated with a serial attached SCSI (SAS) hard disk drive (HDD), and Tier3 is associated with a serial ATA (SATA) HDD.
As a result of the hierarchical control, a volume is provided from the storage apparatus to an external host apparatus. The hierarchical control realizes a real capacity of the volume by allocating a real storage area from each of the tiers within the storage apparatus.
It is hidden from a user (host apparatus) of the volume how the real storage area is allocated to the volume from each of the tiers by the hierarchical control within the storage apparatus. As a result, the host apparatus can handle the volume provided by the storage apparatus equivalently to a storage area of the storage device mounted to the host apparatus.
In the hierarchical control, data is relocated by migrating the data to another tier within the volume. This allows the data to be stored in the tier appropriate based on the utility value of the data.
For example, US 2011/0246739 A1 (Patent Literature 1) discloses a hierarchical control technology in which a unit of the storage area called “page” is defined and the real storage area is allocated to the volume in units of pages. Patent Literature 1 also discloses a method involving relocating the data by migrating data between tiers.